(1) Field of the Invention
This invention relates to an anion exchanger, a process for producing the anion exchanger, and a packing for chromatography comprised of the anion exchanger.
(2) Description of the Related Art
Fine particles having an ion exchanging group are widely used as a separating material in the field of pure water production and chromatography. An anion exchanger having introduced therein polyethyleneimine as an ion exchanging group is used in the field of chelate resins, liquid chromatography for analyzing or isolating, for example, amino acids, peptide, protein, nucleic acids and saccharides.
As examples of the method of making an anion exchanger comprised of a fine particle having introduced therein polyethyleneimine, there can be mentioned a method of introducing polyethyleneimine to a fine particle of a polymer having a halogenated alkyl group such as polychromethylstyrene as disclosed in U.S. Pat. No. 4,191,814; a method of introducing polyethyleneimine to an acrylate or methacrylate polymer having an epoxy group or a halogenated alkyl group as disclosed in U.S. Pat. No. 4,111,859; and a method of allowing an inorganic fine particle to adsorb polyethyleneimine and then crosslinking the adsorbed polyethyleneimine as disclosed in U.S. Pat. No. 4,245,005.
The present inventors found that, even when polyethyleneimine having a large molecular weight is introduced to a fine particle having a halogenated alkyl group or an epoxy group, the resulting ion exchanger exhibits an ion exchanging capacity enhanced only to a minor extent. It is presumed that this is because only a minor amount of polyethyleneimine is introduced. If a large amount of polyethyleneimine is added together with a large amount of a crosslinking agent to a liquid dispersion of fine particles to introduce a large amount of polyethyleneimine to the fine particle, the crosslinking of polyethyleneimine proceeds at a high rate and the reaction system undesirably becomes gelled. A similar problem arises in the above-mentioned method described in U.S. Pat. No. 4,245,005. That is, only a minor amount of polyethyleneimine can be adsorbed on fine particles, and, if a large amount of polyethyleneimine is adsorbed on fine particles and then a large amount of a crosslinking agent is added into a liquid dispersion of the polyethyleneimine-adsorbed fine particles, the liquid dispersion tends to be gelled at the crosslinking step. Therefore, the amounts of polyethyleneimine and a crosslinking agent used are restricted.
In view of the foregoing, an object of the present invention is to provide an anion exchanger which exhibits an enhanced anion exchanging capacity, and which can be advantageously made without tendency of gelling even by using relatively large amounts of polyethyleneimine and a crosslinking agent are used as compared with the conventional method using polyethyleneimine and a crosslinking agent.
Another object of the present invention is to provide a process for producing the above-mentioned anion exchanger exhibiting an enhanced anion exchanging capacity, which can be advantageously conducted without tendency of gelling even by using relatively large amounts of polyethyleneimine and a crosslinking agent are used.
Still another object of the present invention is to provide a packing for chromatography comprised of the above-mentioned anion exchanger exhibiting an enhanced anion exchanging capacity.
A further object of the present invention is to provide a column for chromatography packed with a packing comprised of the above-mentioned anion exchanger exhibiting an enhanced anion exchanging capacity.
In one aspect of the present invention, there is provided an anion exchanger which is a fine particle having a cured surface layer formed on the surface of the fine particle; characterized in that said cured surface layer is comprised of a crosslinked polyethyleneimine and is capable of being formed by the following steps (1) and (2):
(1) a first step of dispersing a fine particle having a functional group capable of reacting with polyethyleneimine on the surface of the fine particle, in an aqueous solution of a crosslinking agent capable of crosslinking polyethyleneimine to prepare an aqueous dispersion of the fine particle; and
(2) a second step of adding the polyethyleneimine and a catalyst for crosslinking the polyethyleneimine in the aqueous dispersion of the fine particle, and carrying a reaction of bonding the polyethyleneimine to the functional group on the fine particle surface and a reaction of crosslinking the polyethyleneimine with the crossslinking agent.
In another aspect of the present invention, there is provided a process for producing an anion exchanger which is a fine particle having a cured surface layer comprised of crosslinked polyethyleneimine and formed on the surface of the fine particle, characterized by comprising the steps of:
(1) a first step of dispersing a fine particle having a functional group capable of reacting with polyethyleneimine on the surface of the fine particle, in an aqueous solution of a crosslinking agent capable of crosslinking polyethyleneimine to prepare an aqueous dispersion of the fine particle; and
(2) a second step of adding the polyethyleneimine and a catalyst for crosslinking the polyethyleneimine in the aqueous dispersion of the fine particle, and carrying a reaction of bonding the polyethyleneimine to the functional group on the fine particle surface and a reaction of crosslinking the polyethyleneimine with the crossslinking agent.
The polyethyleneimine used preferably has a number average molecular weight of not larger than 10,000, more preferably not larger than 1,000, and has a functional group on the fine particle surface which is preferably at least one member selected from a glycidyl group, a halogenated alkyl group and an aldehyde group. The fine particle is preferably a porous particle having pores with an average diameter of at least 100 xc3x85. The crosslinking agent is preferably epichlorohydrin or a polyfunctional epoxy compound such as ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, 1,4-butanediol diglycidyl ether, glycerol polyglycidyl ether or sorbitol polyglycidyl ether. The catalyst used for crosslinking is preferably an alkali metal hydroxide.
In still another aspect of the present invention, there is provided a packing for chromatography, which is comprised of the above-mentioned anion extender.
In a further aspect of the present invention, there is provided a column for chromatography, which is packed with the above-mentioned packing.